Butadiene is an important basic raw material in the petrochemical industries, and is widely used in the production of many synthetic rubbers, including polybutadiene rubber, styrene-butadiene rubber, butadiene-acrylonitrile rubber and butadiene rubber, wherein polybutadiene rubber is a main material for the production of tyres. Furthermore, butadiene is widely used in the syntheses of resins, fibers and fine chemical products. For example, butadiene can be used in the production of many coatings.
In the prior art, butadiene was ever produced mainly by separating C4 fractions, which were main by-products from the production of ethylene through hydrocarbon cracking. However, in recent years, with the change in the structure of the energy sources, C1 chemical industry, shale gas and the like were developed soon so that the production of butadiene from hydrocarbon cracking was reduced gradually, whereas the downstream industries of butadiene were developed soon so that the demand of butadiene was increased continuously. In such a situation, the process for producing butadiene by oxidative dehydrogenation of butylene was developed and more and more attention was attracted gradually.
In the oxidative dehydrogenation butylene is oxidized and dehydrogenated with oxygen to form butadiene in the presence of a catalyst, and the resultant product comprises butadiene as the primary product and some by-products such as carbon dioxide, carbon monoxide, hydrogen and oxygenates including aldehydes, ketones, acids and the like. Due to the presence of the by-products, the resultant product needs to be post-treated, including first heat recovery and water scrubbing to recover the reaction heat and remove most oxygenates, then compression (generally multi-stage compression) and oil absorption-desorption to separate raw butadiene, and final butadiene extraction to obtain finished butadiene suitable for industries subsequently.
The suitable reactors for oxidative dehydrogenation of butylene generally comprise a fluidized bed and an adiabatic fixed bed, wherein the fluidized bed has a problem that the catalyst used therein may have to be strong enough to resist the abrasion during the fluidization, whereas the adiabatic fixed bed has more simple requirements for the catalyst, thus being widely used in the oxidative dehydrogenation of butylene.
When being used in the oxidative dehydrogenation of butylene to butadiene, the adiabatic fixed bed is generally in the form of multi-stage adiabatic fixed bed, typically of two- or three-stage adiabatic fixed bed, wherein butylene, water and oxygen-comprising gas as the feed are reacted over the catalyst. In such a situation, in order to control the temperature in the catalyst bed within a suitable range, a lot of steam is needed, so high energy consumption is necessary.
CN101367702A disclosed a process for producing butadiene by oxidative dehydrogenation of butylene using an axial fixed bed, wherein a two-stage axial fixed bed is used to produce butadiene from a feed comprising butylene, air and steam, wherein an intermediate heat exchanger is provided between the two stages of the fixed bed to heat the steam to the first stage of the fixed bed through heat exchanging with the effluent from the first stage of the fixed bed.
CN102516008A disclosed a new process for oxidative dehydrogenation, wherein a two-stage fixed bed is used to produce butadiene from a feed comprising butylene, steam and oxygen-enriched air, wherein the conversion of butylene is improved by the oxygen-enriched air, and the effluent from the reactor has a reduced nitrogen amount due to the less nitrogen in the oxygen-enriched air, thus the oil absorption unit has a reduced oil consumption, but more steam is needed in the feed to control the temperature in the catalyst bed due to the reduced nitrogen amount in the feed.
CN103964996A disclosed an energy-saving process for produce butadiene by oxidative dehydrogenation of butylene with a primary target of reducing the steam consumption during the reaction, wherein a multi-stage fixed bed in series is used, and the reaction heat is recovered via intermediate heat exchanger(s).
CN103964998A disclosed a process for improving the yield of butadiene during the oxidative dehydrogenation of butylene, wherein a multi-stage fixed bed in series is used with all the steam being fed into the first stage of the fixed bed and the feed comprising butylene and the oxygen-comprising gas being fed to each stage of the fixed bed respectively and proportionally, wherein each stage of the fixed bed is packed with layers of various catalysts having different activities for converting different butylene isomers, thus improving the total conversion of butylene and the yield of butadiene.
CN104772081A disclosed a process for catalyst-packing a multi-stage adiabatic fixed bed for producing butadiene by oxidative dehydrogenation of butylene, wherein a multi-stage adiabatic fixed bed in series is used and each stage of the adiabatic fixed bed comprises two reaction zones, which are packed with different catalyst respectively, thus converting butylene to butadiene better and improving the total conversion of butylene and the yield of butadiene.
With regard to the catalytic reaction for producing butadiene by oxidative dehydrogenation of butylene, the adiabatic fixed bed widely used in the prior art is found still with problems such as higher steam consumption, higher power consumption of the compressor, higher load of the oil absorption unit and the like, after comprehensively estimating the total energy consumption of the reaction system and the post treatment system (including heat recovery, water scrubbing, compression of the reaction gas, oil absorption-desorption and the like). Thus, it is still desirable to further reduce the total energy consumption of the process to improve the economy thereof.